We describe a unique case of a bilateral osteochondrosis of the femoral heads, similar to Perthes disease, in a boy affected by Alagille syndrome. This is a rare genetic syndrome, caused by vascular anomalies, and characterized by five main features: hepatic, cardiovascular, ophthalmological, skeletal malformations, and characteristic facial appearance. The most frequent skeletal finding is the 'butterfly vertebra'. We have followed the patient from the age of 5 years to the age of 20 years. We performed two bilateral valgus osteotomies when he was 10 years old to limit the progression of the deformity. We believe that the association of a bilateral osteochondrosis of the femoral heads with Alagille syndrome, a disease characterized by a vascular etiology, supports the hypothesis of angiogenic pathogenesis of Perthes disease.